The invention is based on a sliding-link mechanism such as has already been proposed for actuating a throttle valve in the intake tube of an internal combustion engine. There, the position of the throttle valve is adjusted with a predetermined quantity of air, resulting in various positions for the variable-fulcrum lever. Given the various dimensional tolerances of the individual parts, the roller disposed on the roller lever then is no longer located in the correct position in the oblong slot groove of the variable-fulcrum lever, thereby resulting in a distortion of the desired movement.